This invention relates to a method of adjusting the balance of the rotor of a vehicle AC generator.
FIG. 2 is a sectional view showing a vehicle AC generator which is driven, for instance, by the engine of an automobile. In FIG. 2, reference numeral 1 designates a stator; 4, a rotor. The stator comprises: a stator core 2, and a stator coil assembly 3. The rotor 4 comprises: magnetic pole cores 5 and 6 opposite in polarity, which have magnetic pole claws 5a and 6a, respectively, which, being arranged at equal angular intervals, are intertwined; an exciting coil assembly 7 held between the magnetic pole cores 5 and 6; a rotary shaft 8 on which the magnetic pole cores 5 and 6 are fixedly mounted; a pair of slip rings 9 mounted through insulating sleeves on the rotary shaft 8; and fans 10 and 11 secured to the magnetic poles 5 and 6, respectively.
Further in FIG. 2, reference numerals 12 and 13 designate a front bracket and a rear bracket, respectively, which are combined with the stator core 2 with tightening bolts 14. The front bracket 12 has a plurality of air inlet holes 12a and a plurality of air outlet holes 12b for ventilation. Similarly, the rear bracket 13 has a plurality of air inlet holes 13a and a plurality of air outlet holes 13b for ventilation. The rotary shaft 8 is supported through bearings 15 and 16 on the front bracket 12 and the rear bracket 13. A pulley 17 is fixedly mounted on the rotary shaft 8, so that rotation of the engine is transmitted through an endless belt to the pulley 17 to rotate the rotary shaft 8.
Further in FIG. 2, reference numeral 18 designates a commutator for converting AC current due to AC voltage inducted in the stator coil assembly 3 into DC current; 19, a voltage regulator for detecting a generator voltage, to control exciting current, thereby to regulate a terminal voltage to a predetermined value; and 20, brush holders for holding brushes 21 and pushing the latter against the slip rings 9.
When, in the AC generator thus constructed, the rotor 4 is rotated, AC voltage is inducted in the stator coil assembly 3; that is, the AC generator supplies electric power and produces heat. In this case, the fans 10 and 11 are also rotated to ventilate the generator, thus cooling the stator 1 and the rotor 4.
If, in the AC generator, the amount of unbalance of the rotor 4 is large, then the rotor 4 is greatly vibrated when rotated at high speed, so that it may contact the stator core 2 or at worst damage it. Hence, it is essential to adjust the balance of the rotor 4 to minimize the amount of unbalance of the latter.
A conventional method of adjusting the balance of a rotor will now be described with reference to FIG. 3. In FIG. 3, reference numerals 31 and 32 designate a pair of drills which are arranged in such a manner that they forms an interpole angle A. The drills 31 and 32 are connected to drill driving means in an automatic balance adjusting device (not shown). The aforementioned interpole angle A is the angle which adjacent magnetic pole claws 5a of the stator core 5 form with respect to the center of the latter 5. The rotor 4 is turned with the automatic balance adjusting device, so that an amount of unbalance W thereof and its direction are detected. With the amount of unbalance W as a central composite force, components U and V on the lines defining the interpole angle A, positions on the outer cylindrical surfaces of the magnetic pole claws 5a where holes are to be drilled, and the depth of the holes at the positions are calculated, to provide instruction signals. In response to the instruction signals, holes are automatically formed, as indicated at 28, with the drills 31 and 32, to correct the unbalance of the rotor.
When the above-described conventional rotor balance adjusting method is employed to form holes in the outer cylindrical surfaces of the magnetic core 5 as was described above, the holes may be positioned at any points in the range of an angle B corresponding to the circumferential width of each magnetic pole claw 5a. Hence, the holes are not uniform in depth, depending on the positions thereof (the depth of the hole is decreased as its position is shifted to an end of the circumferential width of the magnetic pole claw 5a). Thus, adjustment of the balance is relatively low in accuracy, and is sometimes difficult.
On the other hand, it is necessary to remove burrs formed by drilling. However, if, in this case, the drilled hole 18 is located near the end of the circumferential width of the outer peripheral surface of the magnetic pole claw 5a, then it is rather difficult to remove the burrs. In addition, the position of the hole is arbitrary as was described above. Hence, in the case where the balance adjusting operation is carried out repeatedly to improve the accuracy of the balance, the drilled holes overlap one another irregularly in the outer peripheral surfaces of the magnetic pole claws 5a in a circumferential direction. In order to overcome this difficulty, the correcting surfaces must be shifted axially.
Furthermore, since the drills 31 and 32 are so held as to form the interpole angle A, the conventional method cannot be applied to other rotors different in the number of poles.